Qt下使用ModbusTcp通信协议进行PLC线圈/保持寄存器的读写（32位有符号数）

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前言

本文主要讲述了使用Qt的Modbus模块来进行ModbusTcp的通信，实现对PLC的线圈寄存器和保持寄存器的读写，基于TCP/IP的Modbus协议的内容我就不做过多解释了，详见参考文章。在本文示例中采用QModbusTcpClient类作为Modbus客户端（主站），PLC作为从站，封装了一个自己的MyModbus类，希望可以帮助到大家，如有错误之处，欢迎大家批评指正。

项目效果

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提示：以下是本篇文章正文内容，下面案例可供参考

一、引入Modbus模块

1.这里我实现了自己的MyModbus类的封装，使用了pri子模块的方式，也是方便日后进行此模块的复用
pri中引入Modbus模块：
MyModbus.pri

QT   += serialbus serialport

MyModbus类中添加相关头文件

#include <QModbusTcpClient>
#include <QModbusDataUnit>

二、Modbus设备的连接

1.ModbusTcp的连接只需要配置好连接参数IP+Port

//判断当前连接状态是否为断开状态
if(myClient->state() != QModbusDevice::ConnectedState)
{//配置ModbusTcp的连接参数IP+PortmyClient->setConnectionParameter(QModbusDevice::NetworkAddressParameter,ip);myClient->setConnectionParameter(QModbusDevice::NetworkPortParameter,port);myClient->connectDevice();
}

三、各寄存器数据的读取

1.Modbus中有4种操作对象，这4种都能进行读取操作：线圈、离散输入、保持寄存器、输入寄存器

//读取modbus设备各寄存器数据
//typeNum:1_线圈 2_离散输入 3_保持 4_输入
bool MyModbus::readModbusData(int typeNum,int startAdd,quint16 numbers)
{if(myClient->state() != QModbusDevice::ConnectedState){return false;}//确定寄存器类型QModbusDataUnit ReadUnit;if(typeNum == 1){ReadUnit = QModbusDataUnit(QModbusDataUnit::Coils,startAdd,numbers);}else if(typeNum == 2){ReadUnit = QModbusDataUnit(QModbusDataUnit::DiscreteInputs,startAdd,numbers);}else if(typeNum == 3){ReadUnit = QModbusDataUnit(QModbusDataUnit::HoldingRegisters,startAdd,numbers);}else if(typeNum == 4){ReadUnit = QModbusDataUnit(QModbusDataUnit::InputRegisters,startAdd,numbers);}else{LOGDEBUG<<"读取寄存器类型错误";return false;}LOGDEBUG<<"readModbusData typeNum:"<<typeNum;//多读if(auto *reply = myClient->sendReadRequest(ReadUnit,1)){if(!reply->isFinished()){if((typeNum == 1) || (typeNum == 2)){QObject::connect(reply,&QModbusReply::finished,this,&MyModbus::slot_readReadyCoils);   //读取线圈}if((typeNum == 3) || (typeNum == 4)){QObject::connect(reply,&QModbusReply::finished,this,&MyModbus::slot_readReadyRegisters);   //读取寄存器}//reply->deleteLater();return true;}else{reply->deleteLater();return false;}}else{LOGDEBUG<<"读取错误:" + myClient->errorString();return false;}
}

四、各寄存器数据的写入

1.Modbus中4种操作对象只有这2种能进行写入操作：线圈 、保持寄存器

//对modbus设备各寄存器写入数据
//typeNum:1_线圈 2_保持 (这两类寄存器可读可写,其余的只读)
bool MyModbus::writeModbusData(int typeNum,int startAdd,int writeNum)
{if(myClient->state() != QModbusDevice::ConnectedState){return false;}//确定寄存器类型QModbusDataUnit writeUnit;if(typeNum == 1){writeUnit = QModbusDataUnit(QModbusDataUnit::Coils,startAdd,1);   //写入一个数据writeUnit.setValue(0,writeNum);//单写//bool ok;//quint16 hexData = writeData.toInt(&ok,16);   //转16进制}else if(typeNum == 2){writeUnit = QModbusDataUnit(QModbusDataUnit::HoldingRegisters,startAdd,2);   //写入两个数据quint16 uData16[2] = {0};uData16[0] = writeNum & 0xffff;uData16[1] = (writeNum >> 16) & 0xffff;writeUnit.setValue(0,uData16[0]);writeUnit.setValue(1,uData16[1]);//LOGDEBUG<<"uData16[0]:"<<uData16[0]<<"   uData16[1]:"<<uData16[1]<<"   writeNum:"<<writeNum;}else{LOGDEBUG<<"写入寄存器类型错误";return false;}//LOGDEBUG<<"writeModbusData typeNum:"<<typeNum<<"   writeNum:"<<writeNum;if(auto *reply = myClient->sendWriteRequest(writeUnit,1)){if(!reply->isFinished()){connect(reply,&QModbusReply::finished,this,[reply](){if(reply->error() == QModbusDevice::NoError){reply->deleteLater();return true;}else{LOGDEBUG<<"写入返回错误:"<<reply->error();reply->deleteLater();return false;}});}else{reply->deleteLater();return false;}}else{LOGDEBUG<<"写入错误:" + myClient->errorString();return false;}return true;
}

五、示例完整代码

这里是示例项目的完整代码，包含pro主程序和MyModbus.pri子文件
1.ModbusTest.pro

QT   += core guigreaterThan(QT_MAJOR_VERSION, 4): QT += widgetsCONFIG += c++11#定义编译选项.QT_DEPRECATED_WARNINGS表示当Qt的某些功能被标记为过时的,那么编译器会发出警告.
DEFINES += QT_DEPRECATED_WARNINGS#设置字符(MSCV编译器下防止中文乱码)
contains( CONFIG,"msvc" ):QMAKE_CXXFLAGS += /source-charset:utf-8 /execution-charset:utf-8
contains( CONFIG,"msvc" ):QMAKE_CFLAGS +=/source-charset:utf-8 /execution-charset:utf-8include (./MyModbus/MyModbus.pri)SOURCES += \main.cpp \widget.cppHEADERS += \widget.hFORMS += \widget.ui# Default rules for deployment.
qnx: target.path = /tmp/$${TARGET}/bin
else: unix:!android: target.path = /opt/$${TARGET}/bin
!isEmpty(target.path): INSTALLS += target

2.MyModbus.pri

QT       += serialbus serialportHEADERS += \$$PWD/mymodbus.hSOURCES += \$$PWD/mymodbus.cpp

3.mymodbus.h

#ifndef MYMODBUS_H
#define MYMODBUS_H#include <QObject>
#include <QModbusTcpClient>
#include <QModbusDataUnit>
#include <QDebug>#define LOGDEBUG qDebug()<<__FILE__<<__LINE__class MyModbus : public QObject
{Q_OBJECT
public:explicit MyModbus(QObject *parent = nullptr);~MyModbus();void initModbus();void connectToModbus(QString ip,int port);bool readModbusData(int typeNum,int startAdd,quint16 numbers);bool writeModbusData(int typeNum,int startAdd,int writeNum);signals:void signal_stateChanged(bool flag);void signal_readCoils(QVector<quint16> vAllData);void signal_readRegisters(int resultNum);private slots:void slot_stateChanged();void slot_readReadyCoils();void slot_readReadyRegisters();private:QModbusTcpClient *myClient;};
#endif // MYMODBUS_H

4.mymodbus.cpp

#include "mymodbus.h"MyModbus::MyModbus(QObject *parent) : QObject(parent)
{this->initModbus();
}MyModbus::~MyModbus()
{}//初始化
void MyModbus::initModbus()
{myClient = new QModbusTcpClient();//connect(myClient,SIGNAL(stateChanged()),this,SLOT(slot_stateChanged()));connect(myClient,&QModbusClient::stateChanged,this,&MyModbus::slot_stateChanged);
}//连接到modbus设备
void MyModbus::connectToModbus(QString ip,int port)
{if(!myClient){return;}//判断当前连接状态是否为断开状态if(myClient->state() != QModbusDevice::ConnectedState){//配置ModbusTcp的连接参数IP+PortmyClient->setConnectionParameter(QModbusDevice::NetworkAddressParameter,ip);myClient->setConnectionParameter(QModbusDevice::NetworkPortParameter,port);myClient->connectDevice();}//else//{//    myClient->disconnectDevice();//}
}//读取modbus设备各寄存器数据
//typeNum:1_线圈 2_离散输入 3_保持 4_输入
bool MyModbus::readModbusData(int typeNum,int startAdd,quint16 numbers)
{if(myClient->state() != QModbusDevice::ConnectedState){return false;}//确定寄存器类型QModbusDataUnit ReadUnit;if(typeNum == 1){ReadUnit = QModbusDataUnit(QModbusDataUnit::Coils,startAdd,numbers);}else if(typeNum == 2){ReadUnit = QModbusDataUnit(QModbusDataUnit::DiscreteInputs,startAdd,numbers);}else if(typeNum == 3){ReadUnit = QModbusDataUnit(QModbusDataUnit::HoldingRegisters,startAdd,numbers);}else if(typeNum == 4){ReadUnit = QModbusDataUnit(QModbusDataUnit::InputRegisters,startAdd,numbers);}else{LOGDEBUG<<"读取寄存器类型错误";return false;}LOGDEBUG<<"readModbusData typeNum:"<<typeNum;//多读if(auto *reply = myClient->sendReadRequest(ReadUnit,1)){if(!reply->isFinished()){if((typeNum == 1) || (typeNum == 2)){QObject::connect(reply,&QModbusReply::finished,this,&MyModbus::slot_readReadyCoils);   //读取线圈}if((typeNum == 3) || (typeNum == 4)){QObject::connect(reply,&QModbusReply::finished,this,&MyModbus::slot_readReadyRegisters);   //读取寄存器}//reply->deleteLater();return true;}else{reply->deleteLater();return false;}}else{LOGDEBUG<<"读取错误:" + myClient->errorString();return false;}
}//对modbus设备各寄存器写入数据
//typeNum:1_线圈 2_保持 (这两类寄存器可读可写,其余的只读)
bool MyModbus::writeModbusData(int typeNum,int startAdd,int writeNum)
{if(myClient->state() != QModbusDevice::ConnectedState){return false;}//确定寄存器类型QModbusDataUnit writeUnit;if(typeNum == 1){writeUnit = QModbusDataUnit(QModbusDataUnit::Coils,startAdd,1);   //写入一个数据writeUnit.setValue(0,writeNum);//单写//bool ok;//quint16 hexData = writeData.toInt(&ok,16);   //转16进制}else if(typeNum == 2){writeUnit = QModbusDataUnit(QModbusDataUnit::HoldingRegisters,startAdd,2);   //写入两个数据quint16 uData16[2] = {0};uData16[0] = writeNum & 0xffff;uData16[1] = (writeNum >> 16) & 0xffff;writeUnit.setValue(0,uData16[0]);writeUnit.setValue(1,uData16[1]);//LOGDEBUG<<"uData16[0]:"<<uData16[0]<<"   uData16[1]:"<<uData16[1]<<"   writeNum:"<<writeNum;}else{LOGDEBUG<<"写入寄存器类型错误";return false;}//LOGDEBUG<<"writeModbusData typeNum:"<<typeNum<<"   writeNum:"<<writeNum;if(auto *reply = myClient->sendWriteRequest(writeUnit,1)){if(!reply->isFinished()){connect(reply,&QModbusReply::finished,this,[reply](){if(reply->error() == QModbusDevice::NoError){reply->deleteLater();return true;}else{LOGDEBUG<<"写入返回错误:"<<reply->error();reply->deleteLater();return false;}});}else{reply->deleteLater();return false;}}else{LOGDEBUG<<"写入错误:" + myClient->errorString();return false;}return true;
}//监听TCP连接的状态,若状态发生改变,发出对应的信号
void MyModbus::slot_stateChanged()
{LOGDEBUG<<myClient->state();if(myClient->state() == QModbusDevice::ConnectedState){emit signal_stateChanged(true);}else if(myClient->state() == QModbusDevice::UnconnectedState){emit signal_stateChanged(false);}
}//接收到读取线圈/离散输入寄存器请求后执行的槽函数
void MyModbus::slot_readReadyCoils()
{QVector<quint16> vAllData;QModbusReply *reply = qobject_cast<QModbusReply *>(sender());if(!reply){LOGDEBUG<<"读取线圈/离散输入寄存器错误";return;}if(reply->error() == QModbusDevice::NoError){const QModbusDataUnit unit = reply->result();vAllData = unit.values();emit signal_readCoils(vAllData);}else{LOGDEBUG<<"线圈/离散输入寄存器回复错误:"<<reply->error();}reply->deleteLater();
}//接收到读取保持/输入寄存器请求后执行的槽函数
void MyModbus::slot_readReadyRegisters()
{QModbusReply *reply = qobject_cast<QModbusReply *>(sender());if(!reply){LOGDEBUG<<"读取保持/输入寄存器错误";return;}if(reply->error() == QModbusDevice::NoError){const QModbusDataUnit unit = reply->result();auto valueList = unit.values();int nSize = valueList.size();if(nSize == 2){quint16 uData16[2] = {0};uData16[0] = valueList[0];uData16[1] = valueList[1];int resultNum = uData16[0] | (uData16[1] << 16);//LOGDEBUG<<"uData16[0]:"<<uData16[0]<<"   uData16[1]:"<<uData16[1]<<"   resultNum:"<<resultNum;emit signal_readRegisters(resultNum);}else{LOGDEBUG<<"保持寄存器返回数据错误,个数:"<<nSize;}}else{LOGDEBUG<<"保持/输入寄存器回复错误:"<<reply->error();}reply->deleteLater();
}/*
//读取保持/输入寄存器数据的另一种方式,已废弃
//当前数据格式为大端模式,高位存低地址
//判断正负数,以高8位的16进制是否为f判断
int resultNum = 0;
if(QString::number(valueList[1],16).left(1) == "f")   //负数
{//判断是否小于-65535,高16位的10进制为65535if(valueList[1] == 65535){resultNum = valueList[0] - 65536;}else{resultNum = (valueList[1] - 65535) * 65536 + (valueList[0] - 65536);}
}
else
{//判断是否大于65535,高16位的10进制大于0if(valueList[1] > 0){resultNum = valueList[1] * 65536 + valueList[0];}else{resultNum = valueList[0];}
}
*/

5.widget.h

#ifndef WIDGET_H
#define WIDGET_H#include <QWidget>
#include <QFileDialog>
#include <QDateTime>
#include <QMessageBox>
#include "MyModbus/mymodbus.h"QT_BEGIN_NAMESPACE
namespace Ui { class Widget; }
QT_END_NAMESPACEclass Widget : public QWidget
{Q_OBJECTpublic:Widget(QWidget *parent = nullptr);~Widget();void initWidget();private slots:void slot_stateChanged(bool flag);void slot_readCoils(QVector<quint16> vAllData);void slot_readRegisters(int resultNum);private slots:void on_pb_connect_clicked();void on_pb_readM_clicked();void on_pb_writeM_clicked();void on_pb_readD_clicked();void on_pb_writeD_clicked();private:Ui::Widget *ui;MyModbus *m_myModsbus;   //MyModbus对象};
#endif // WIDGET_H

6.widget.cpp

#include "widget.h"
#include "ui_widget.h"Widget::Widget(QWidget *parent): QWidget(parent), ui(new Ui::Widget)
{ui->setupUi(this);this->initWidget();
}Widget::~Widget()
{delete ui;
}void Widget::initWidget()
{//初始化MyModbus对象m_myModsbus = new MyModbus();connect(m_myModsbus,SIGNAL(signal_stateChanged(bool)),this,SLOT(slot_stateChanged(bool)));connect(m_myModsbus,SIGNAL(signal_readCoils(QVector<quint16>)),this,SLOT(slot_readCoils(QVector<quint16>)));connect(m_myModsbus,SIGNAL(signal_readRegisters(int)),this,SLOT(slot_readRegisters(int)));}void Widget::slot_stateChanged(bool flag)
{if(flag){ui->lb_state->setText("连接成功");ui->te_show->appendPlainText(QTime::currentTime().toString("hh:mm:ss: ") + "连接成功");QMessageBox::warning(this,"警告","连接成功!");}else{ui->lb_state->setText("连接断开");ui->te_show->appendPlainText(QTime::currentTime().toString("hh:mm:ss: ") + "连接断开");QMessageBox::warning(this,"警告","连接断开!");}
}void Widget::slot_readCoils(QVector<quint16> vAllData)
{LOGDEBUG<<"readCoils size:"<<vAllData.size();for(int i=0;i<vAllData.size();i++){LOGDEBUG<<"i:"<<vAllData[i];ui->te_show->appendPlainText(QTime::currentTime().toString("hh:mm:ss: ") + "读取M区返回数据:" + QString::number(vAllData[i]));ui->le_dataM->setText(QString::number(vAllData[0]));}
}void Widget::slot_readRegisters(int resultNum)
{LOGDEBUG<<"resultNum:"<<resultNum;ui->te_show->appendPlainText(QTime::currentTime().toString("hh:mm:ss: ") + "读取D区返回数据:" + QString::number(resultNum));ui->le_dataD->setText(QString::number(resultNum));
}void Widget::on_pb_connect_clicked()
{QString ip = ui->le_ip->text();int port = ui->le_port->text().toInt();LOGDEBUG<<"ip:"<<ip<<"   port:"<<port;ui->te_show->appendPlainText(QTime::currentTime().toString("hh:mm:ss: ") + "ip:" + ip + " port:" + QString::number(port));//连接到modbus设备m_myModsbus->connectToModbus(ip,port);
}void Widget::on_pb_readM_clicked()
{int startAdd = ui->le_addressM->text().toInt();LOGDEBUG<<"startAdd:"<<startAdd;if(!m_myModsbus->readModbusData(1,startAdd,1)){QMessageBox::warning(this,"警告","M区数据读取失败!");}
}void Widget::on_pb_writeM_clicked()
{int startAdd = ui->le_addressM->text().toInt();int writeNum = ui->le_dataM->text().toInt();LOGDEBUG<<"startAdd:"<<startAdd<<"   writeNum:"<<writeNum;//单写if(!m_myModsbus->writeModbusData(1,startAdd,writeNum)){QMessageBox::warning(this,"警告","M区数据写入失败!");}
}void Widget::on_pb_readD_clicked()
{int startAdd = ui->le_addressD->text().toInt();LOGDEBUG<<"startAdd:"<<startAdd;if(!m_myModsbus->readModbusData(3,startAdd,2)){QMessageBox::warning(this,"警告","D区数据读取失败!");}
}void Widget::on_pb_writeD_clicked()
{int startAdd = ui->le_addressD->text().toInt();int writeNum = ui->le_dataD->text().toInt();;LOGDEBUG<<"startAdd:"<<startAdd<<"   writeNum:"<<writeNum;//进行写入寄存器数据的处理if(!m_myModsbus->writeModbusData(2,startAdd,writeNum)){QMessageBox::warning(this,"警告","D区数据写入失败!");}
}

7.main.cpp

#include "widget.h"
#include <QApplication>
#include <QMutex>//程序输出日志
void outputMessage(QtMsgType type,const QMessageLogContext &context,const QString &msg)
{static QMutex mutex;mutex.lock();//初始化log文件夹QString logFilePath = QCoreApplication::applicationDirPath() + "/LogFile/";QDir dstDir(logFilePath);if(!dstDir.exists()){if(!dstDir.mkpath(logFilePath)){LOGDEBUG<<"程序输出日志创建失败！";}else{LOGDEBUG<<"程序输出日志创建成功！";}}//获取输出内容QString debugMsg;if(type == QtDebugMsg){QString debugDateTime = QDateTime::currentDateTime().toString("yyyy-MM-dd hh:mm:ss");debugMsg = QString("%1\n%2%3").arg(debugDateTime).arg(msg).arg(context.function);}//保存文件QString curDate = QDate::currentDate().toString("yyyyMMdd");QString logFile = logFilePath + "log_" + curDate + ".txt";QFile file(logFile);file.open(QIODevice::WriteOnly | QIODevice::Append);QTextStream textStream(&file);textStream << debugMsg << "\n\n";file.flush();file.close();mutex.unlock();
}int main(int argc, char *argv[])
{QApplication a(argc, argv);qInstallMessageHandler(outputMessage);Widget w;w.show();return a.exec();
}

8.widget.ui

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总结

基于Qt使用这个ModbusTcp协议进行通信，还是比较简单的，首先就是确定下寄存器的类型，直接使用相关的函数进行读写。需要注意的一点是在进行保持寄存器读写的时候，我们PLC某个地址上的数是个16位的数，所以在进行32位有符号数读写的时候，要考虑两个相邻地址的组合，文中就对此进行了处理，这种情况下PLC那边也别忘记进行相应的设置哈。

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hello：
共同学习，共同进步，如果还有相关问题，可在评论区留言进行讨论。

参考博客：
QT下的Modbus TCP 通讯
C++与PLC通过Modbus TCP协议进行PLC内部寄存器的值的读取/写入总结